Gaseous discharge lamp circuit employing a pulser and a saturable reactor



July 22, 1969 F. w. PAGET ET AL 3,457,458

QASEOUS DISCHARGE LAMP CIRCUIT EMPLOYING A PULSER I AND A SATURABLEREACTOR. Filed July 5, 1967 United States Patent US. Cl. 315-284 4Claims ABSTRACT OF THE DISCLOSURE An electronic circuit having asemiconductor pulse generating circuit for applying ionizing pulses to afluorescent lamp, and an amplifier or thermistor for sensing voltage orcurrent applied to or drawn by the lamp and limiting the amplitude ofthe ionizing pulses inversely dependent on the current.

Conventional fluorescent lamp starting and operating circuits havecomprised a ballast for applying a high starting voltage to the lamp toionize it and start discharge and for inductively limiting currentthrough the ionized lamp. Because of the weight and bulk of the ballastand its high expense, heating and noise, control circuits have beenproposed which start and control the lamp discharge by variouselectronic switching circuits. Some of the advanced electronicallyvalved circuits comprise pulse generating or gating means forperiodically applying a voltage pulse to the lamp thereby ionizing thelamp sufiiciently to support an arc discharge for a limited period,usually a half-cycle or less of the alternating current supply. If theamplitude and duration of the pulse is very precise ly controlled thelamp will tend to extinguish after each pulse application, rather thandraw increasingly greater, run-away current as its negative resistancecharacteristic would otherwise allow.

Despite the above described inherent current control of electronic pulseapplying circuits, it is desirable in some instances to employ furthercurrent limiting, and it is the object of the present invention toprovide a circuit which cooperates with advantageous electronic pulseapplying circuits positively to limit current drawn by a fluorescentlamp.

According to the invention a fluorescent lamp regulating circuitcomprises discharge terminals for connection to a lamp, power terminalsfor connection to a supply of alternating current, a power circuitconnecting said power terminals to said discharge terminals includingmeans for applying periodic voltage pulses to said discharge terminalsthereby to start an arc discharge by ionization in the lamp and to drawcurrent from said alternating current supply dependent on the amount ofionization, a transformer having a secondary in said power circuitconducting said voltage pulses to said discharge terminals, saidtransformer having a primary, means for sensing the amplitude of voltageor current in said power circuit, and means interconnecting said sensingmeans and transformer primary and responsive to said current amplitudeto apply to said primary a direct current thereby changing the inductivereactance or an alternating current inducing in the secondary a voltageopposed to said voltage pulse, thereby to control ionization and limitcurrent drawn by said lamp.

For the purpose of illustration typical embodiments of the invention areshown in the accompanying drawing, in which FIGS. 1 and 2 are schematicdiagrams of two forms of fluorescent lamp regulating circuits.

The regulating circuit of FIG. 1 comprises discharge terminals 1 betweenwhich are connected two four-foot HO lamps L which may be considered asone lamp. Power for the lamps is supplied from 115 volt, 60 cyclealternating current line terminals A and C, terminal C being directlyconnected to one lamp terminal I and terminal A being connected toanother terminal I through an autotransformer primary T1 and secondaryT2, and the secondary T4 of a core transformer having a primary T3. Theautotransformer is of very small reactance, e.g. 47 to ohms at 60cycles, compared to a conventional ballast.

A voltage pulse discharging circuit includes a triac V1 (G.E. typeSC45B), a diac D1 (G.E. type 8T2), a primary voltage pulse storagecapacitor C1 (6 microfarads) a secondary storage capacitor C2 (0.33microfarad) and a coupling capacitor C3 (0.07 microfarad), The primarystorage capacitor C1 and triac V1 are connected in series between thepower terminals A and C through the autotransformer primary T1, so thatduring each half-cycle of alternating current the primary storagecapacitor C1 charges, through the triac V1. In the succeeding halfcyclethe voltage across the secondary capacitor C2 rises toward the breakdownvoltage of the diac D1. When this breakdown voltage is exceeded the diacD1 conducts allowing the secondary capacitor C2 to discharge to the gateelectrode g of the triac and trigger the triac int avalanche conduction.The primary capacitor then discharges through the triac andautotransformer primary and reverses its charge. The discharge voltageis stepped up by the 1 to 3 ratio of primary to secondary, and thestepped up voltage (e.g. 400 volts peak) is applied to the lampterminals I. At this instant a limited number of ions are established inthe lamps L, and the lamp fully ignites and conducts line current forpart or all of the half-cycle. About when the line voltage passesthrough zero the arc tends to extinguish depending on the amplitude andduration of the ionizing pulse. If the pulse becomes too high inamplitude or too long in duration, as by a power surge at terminals Aand C, the lamp, because of its negative resistance characteristic wouldtend to draw increasingly greater current and reach run-away conditioncausing failure of the lamp or some part of the lamp circuit or supply.

According to the present invention, run-away conduction is prevented 'bysensing the current in the circuit or the voltage applied to the circuitand controlling the ionizing voltage pulse inversely dependent on theamplitude of the lamp current. In FIG. 1 the sensing means comprises aconventional alternating current amplifier B of approximately 10 to 15db gain connected between the power terminals A and C in series with theprimary T3 of the core transformer and a resistor R (10,000 ohms). Undernormal line voltage conditions during each half-cycle, the amplifiercauses the primary T3 to apply to the core transformer a flux such as tosomewhat oppose the ionizing voltage pulse. If a surge of line voltageat the power terminals tends to increase the amplitude of the voltagepulse the voltage through the primary is increased opposing the pulseamplitude increase, thereby compensating for the line voltage surge.

In FIG. 2 the sensing means comprises a known photoresistor orthermistor Rt with an integral lamp or heater H, the heater H beingconnected in series with the lamps L. An increase in current drawn bythe arc discharge lamp L ohmically increases the temperature of theheater H causing increased heat or light output and lowers theresistance of the photoresistor of thermistor R2. The resistor Rt iscoupled to a saturable reactor with windings T3 and T4, winding T4 beingin series with the lamps L, and controlling lamp current.

In the circuit of FIG. 2 the components have the same While twodesirable embodiments of the invention have values as the likecomponents in FIG. 1 and are as folherein been disclosed by way ofexample, it is to be unlows: derstood that the invention is broadlyinclusive of any and R1 10,000 Ohms all modifications falling within theterms of the appended R2 500,000 ohms, clalms- R3 15,000 ohms. We R45,000 Ohms 1. A fluorescent lamp regulating circuit comprising:

discharge terminals for connection to a lamp,

C4 microfarads. c5 0.33 microfarad power terrmrtials for connection to asupply of alternat- D2 GE. type sT2. 10 mg a D3 1N456 a power c1rcu1tconnecting said power terminals to said discharge terminals includingmeans for applying V2 G.E. type SC45B.

- periodic voltage pulses to said discharge termmals T3 5,000 turns #42wire.

- thereby to support an arc discharge by ionlzation in T4 300 turns #22wire.

- 11- the lamp and to draw current from said alternating T5 6 henries at50 ma. 0

current supply dependent on the amount of ioniza- Resistor R2 is in onearm of a Voltage divider that sets tion, the Pedestal helght of a p andPedesha1 Control elrcult an inductance having a secondary in said powercircuit R3, D3, R2, C5 D2, V2, R4 and Rll. Cap C5 conducting saidvoltage pulses to said discharge tercharges at a certain rate from theline voltage through rei 1 id i d t having a ima y, sistor R2. This isthe ramp portion of the circuit. At ea h means for sensing th am fimd ofu t i aid half-cycle the ramp voltage is boosted to a variable d epowercircuit, gfee from the Pedesta1 elfelht F Rf That and meansinterconnecting said sensing means and in the Pedestal veltage theJhhetlon 0f Yeslstofs R3 and ductance primary and responsive to saidcurrent am- 15 the startlhg Point for the Steady p voltagethat plitudeto oppose said voltage pulse in the secondary, Charges eaPaeltof ThePedestal Voltage at the l thereby to control ionization and limitcurrent drawn tion of resistors R3 and Rt depends on the value of reby i1 slstol' w the Voltage at h Junction that: 2. A circuit according toclaim 1 wherein said sensing and capacitor C5 fetflches the finhg levelof that? p lt means is connected directly to said power terminals toconducts and fires triac V2. V2 is thus fired later in the Sense hvoltage li d h y e 1f the P e voltage i Smaller h Pedestal t 3. Acircuit according to claim 1 wherein said sensing age is smaller 1fresistor Rt is low in resistance. Thus 11? means Comprises meansconnected to a l i l fo lamp current increases, Rt decreases and triacV2 is fired Sensing the current drawn b h lamp, t p py 4. A circuitaccording to claim 1 wherein said pulse Flllllg triac V2 later in thecycle passes a smaller quangenerating means t f r r Secondary and hmptity of charge per cycle to capacitor C4 through voltage minals areconnected in a closed loop divider resistors R1, R4. Capacitor C4 storescharge and assumes an equilibrium voltage between the bleed-oh of Noreferences cited.

charge by resistor R1 and windings T3 and T5, and the addition of chargethrough resistor R4. Thus the DC level 40 JAMES W. LAWRENCE, PrimaryExaminer applied to winding T3 is under control of Rt. An induc- C RCAMPBELL Assistant Examiner tive reactance T5 prevents alternatingcurrent in the secondary T4 from being coupled into the controllingcircuit. CL

Thus, as lamp current tends to increase, the DC voltage in the WindingT3 decreases and the inductive reactance 3073055 3152895 32389 ofwinding T4 increases and opposes the ionizing voltage pulse and limitsthe conduction of the lamp L.

